1. Field of the Invention
The present invention relates generally to television receivers, and more particularly to television receivers having a still picture reproducing function.
2. Description of the Background Art
Conventional methods for separating a luminance signal (Y signal) and a chrominance signal (C signal) from a composite television signal include a method using a movement adaptation type YC separating circuit.
FIG. 1 is a block diagram showing a construction of a conventional movement adaptation type YC separating circuit disclosed in Japanese Patent Laying-Open No. 61-123295. Referring to FIG. 1, a composite video signal is converted to an 8-bit digital signal by an A/D converter 1. This digital signal is delayed by 1H (H being a horizontal sync signal period) in a line memory 2 and it is further delayed by 524H's in a frame memory 3. Input and output signals of the line memory 2 supplied to a subtracter 4, where the output signal of the line memory 2 is subtracted from the input signal of the line memory 2. A luminance signal component is offset in the output of the subtracter 4 by line correlation of the composite television signal. However, since a high frequency component of the luminance signal in the vertical direction of the screen remains, this component is removed by a horizontal bandpass filter 5. The output of the horizontal bandpass filter 5 is supplied as a first chrominance signal MC to a mixing circuit 9. The output signal of the A/D converter 1 and the first chrominance signal MC are supplied to a subtracter 6, where the first chrominance signal MC is subtracted from the output signal of the A/D converter 1. As a result, the chrominance signal component is offset in the composite television signal as the output signal of the A/D converter 1, whereby a first luminance signal MY is obtained. This first luminance signal MY is supplied to the mixing circuit 9.
In the meantime, the output signal of the A/D converter 1 and the output signal of the frame memory 3 are supplied to a subtracter 7, where the output signal of the frame memory 3 is subtracted from the output signal of the A/D converter 1. Since the output signal of the frame memory 3 is a signal delayed exactly by one frame from the composite video signal outputted from the A/D converter 1, a luminance signal component is offset in the output signal of the A/D converter 1 by frame correlation so that a second chrominance signal SC is obtained. This second chrominance signal SC is supplied to the mixing circuit 9. The output signal of the A/D converter 1 and the second chrominance signal SC are supplied to a subtracter 8, where the second chrominance signal SC is subtracted from the output signal of the A/D converter 1. As a result, the color signal component is offset in the composite video signal outputted from the A/D converter 1, whereby a second luminance signal SY is obtained. The second luminance signal SY is supplied to the mixing circuit 9.
The output signal of the A/D converter 1 and the output signal of the frame memory 3 are supplied to a movement detecting circuit 10. This movement detecting circuit 10 evaluates a difference signal between frames of the composite video signal and determines based on the difference signal- whether an image formed by the present composite video signal is a moving picture or a still picture. The output of the movement detecting circuit 10 is supplied to the mixing circuit 9. The mixing circuit 9 selects the first luminance signal MY and the first chrominance signal MC separated by utilizing the line correlation and outputs those signals as the luminance signal Y and the chrominance signal C if the output of the movement detecting circuit 10 indicates a moving picture. On the other hand, if the output of the movement detecting circuit 10 indicates a still picture, the mixing circuit 9 selects the second luminance signal SY and the second chrominance signal SC separated by utilizing the frame correlation and outputs those signals as the luminance signal Y and the chrominance signal C.
The movement detecting circuit 10 may be constructed to output a detection signal having its level changing in an analog manner according to the moving condition of the picture and the mixing circuit 9 may be constructed to mix the first luminance signal MY and the second luminance signal SY with a ratio according to the level of the detection output and to mix the first chrominance signal MC and the second chrominance signal SC with that ratio.
The above mentioned movement adaptation type YC separating circuit makes it possible to separate a luminance signal and a chrominance signal with high qualities without causing any mixture or remaining of those signals.
If still picture reproduction is to be effected in a television receiver comprising a movement adaptation type YC separation circuit as described above, still picture reproduction processing is conventionally carried out by using a dedicated frame memory. More specifically, a frame memory other than the frame memory provided in the movement adaptation type YC separating circuit is provided to carry out still picture reproduction processing. However, this frame memory dedicated to still picture reproduction processing is very expensive and the use of such a dedicated frame memory is disadvantageous in cost.